Boiler Emissions Testing in Southern California: Rules 1146, 1146.1, and 1147 Explained

If your facility operates a permitted boiler in the South Coast Air Basin, Rules 1146 and 1146.1 dictate your NOx and CO emission limits. These rules affect thousands of units across Southern California -- in hotels, hospitals, schools, manufacturing plants, commercial buildings, and industrial facilities.

The rules aren't new, but they're getting tighter. Amended versions are moving through the SCAQMD rulemaking process, and Rule 1146.2 now extends zero-emission requirements to smaller units. Here's what operators need to know about current requirements and what's ahead.

Rule 1146: Boilers and Heaters 5 MMBtu/hr and Larger

Rule 1146 applies to any boiler, steam generator, or process heater with a rated heat input capacity of 5 million Btu per hour (MMBtu/hr) or greater. These are the larger units found in industrial facilities, hospitals, universities, and large commercial buildings.

Current Emission Limits

Rule 1146 sets emission limits based on the type of unit and its heat input rating. For natural gas-fired units, the current NOx limits are:

• Atmospheric units (5-20 MMBtu/hr): 12 ppm NOx @ 3% O2
• Atmospheric units (>20 MMBtu/hr): 9 ppm NOx @ 3% O2
• Forced draft units: 9 ppm NOx @ 3% O2

CO limits are typically set at 400 ppm @ 3% O2, though some permit conditions impose lower limits depending on the BARCT determination for the specific unit.

These limits assume corrected concentrations at 3% oxygen, which is the standard reference point. Raw stack readings must be corrected to this basis before comparing to the limit.

Testing Requirements

Boilers subject to Rule 1146 must demonstrate compliance through source testing at the following intervals:

• Units rated 10 MMBtu/hr and above: Source test every 3 years
• Units rated 5 to less than 10 MMBtu/hr: Source test every 5 years

The standard test measures NOx, CO, and O2 at minimum. SCAQMD Method 100.1 is the typical method, using portable continuous gas analyzers. Three valid test runs are required, with the average of the three runs compared against the permit limit.

Some larger units are equipped with CEMS (Continuous Emission Monitoring Systems), particularly those that were part of the RECLAIM program. These units have RATA requirements instead of periodic source testing -- but RATA is itself a source test, conducted annually using EPA reference methods.

Operating Conditions During Testing

The boiler must operate at representative conditions during the test. SCAQMD typically requires testing at the higher end of the unit's operating range.

This means coordinating with your operations team and boiler service company. The burner must be tuned and operating properly before the source test. A poorly tuned burner is likely to fail, and a failed test creates a compliance problem.

Rule 1146.1: Boilers and Heaters Greater Than 2 and Less Than 5 MMBtu/hr

Rule 1146.1 covers the mid-range units -- boilers with a rated heat input greater than 2 MMBtu/hr and less than 5 MMBtu/hr. These are common in hotels, apartment complexes, medium-sized commercial buildings, and smaller industrial operations.

Current Emission Limits

For natural gas-fired atmospheric units under Rule 1146.1:

• NOx: 20 ppm @ 3% O2
• CO: 400 ppm @ 3% O2

The NOx limit is higher than Rule 1146 because these smaller units have fewer available retrofit technologies. Still, 20 ppm represents a significant reduction from the older, uncontrolled levels that could exceed 60-80 ppm.

Testing Requirements

Source testing for Rule 1146.1 units follows a 5-year testing cycle. The method and procedure are the same: SCAQMD Method 100.1, three runs, NOx/CO/O2 measured simultaneously.

Many facility managers with smaller boilers don't realize they have source testing obligations. The permit conditions are there, but these units often get overlooked until an SCAQMD inspector visits and asks for the most recent test report. By then, the facility is overdue.

Rule 1146.2: Units 2 MMBtu/hr and Smaller

Rule 1146.2 addresses the smallest boilers and water heaters -- units with a rated heat input of 2 MMBtu/hr or less. This rule has undergone significant amendments and represents the most aggressive regulatory push in this space.

The Zero-Emission Standard

Rule 1146.2 establishes a zero-emission standard for new space and water heating equipment in new construction beginning in 2026. This applies to residential and commercial buildings alike. The practical effect is that new buildings in the South Coast Air Basin will need to install electric heat pump systems rather than gas-fired boilers and water heaters.

For existing units, the rule maintains current NOx emission standards for replacement equipment but signals the district's long-term direction: electrification of small combustion sources.

What This Means for Existing Facilities

If you currently operate small gas-fired boilers or water heaters, Rule 1146.2 doesn't require you to replace them immediately. But when those units reach end-of-life and need replacement, the available options will shift depending on the building type and construction date.

Facilities planning major renovations or new construction should factor this into mechanical system design now. The zero-emission standard isn't a proposal -- it's adopted rule language.

Amended Rules 1146 and 1146.1: What's Coming

SCAQMD has been working on amendments to Rules 1146 and 1146.1, with a public hearing tentatively scheduled for Q1 2026. The proposed amendments could further tighten NOx and CO limits for existing units, expand testing requirements, and align with SCAQMD's broader BARCT obligations under the 2022 AQMP.

While the final rule language isn't set, the direction is clear: lower NOx limits, potentially expanded applicability, and possible changes to testing frequencies. Facilities that are currently in compliance but running close to their permit limits should pay attention. A tightened limit could push a previously passing boiler into non-compliance without any change in the unit's actual performance.

Facility operators should:

• Monitor the rulemaking process. SCAQMD publishes proposed rule amendments and schedules public hearings and workshops.
• Assess current emission levels. If your last source test showed NOx at 10 ppm on a 12 ppm limit, a tightened limit to 9 ppm puts you out of compliance.
• Discuss retrofit options with your boiler service company. Low-NOx burner retrofits, combustion tuning, and flue gas recirculation are established technologies for reducing emissions from existing units.

Who Is Affected

The scope of Rules 1146 and 1146.1 is broad. Any facility in the South Coast Air Basin with a permitted boiler, steam generator, or process heater is potentially subject to these rules. That includes:

• Hotels and resorts -- large hot water and steam boilers for laundry, HVAC, and kitchen operations
• Hospitals and medical centers -- steam boilers for sterilization, heating, and humidification
• Schools and universities -- central plant boilers for campus heating
• Manufacturing facilities -- process heaters, thermal fluid heaters, and steam generators
• Commercial buildings -- HVAC boilers, domestic hot water systems
• Laundries and food processing -- steam boilers running multiple shifts

Many of these facilities rely on boiler maintenance and service companies to keep their units running. Companies like California Boiler and similar service providers handle burner tuning, combustion adjustments, and equipment repairs. Source testing is a separate function that requires a LAP-approved testing company.

The Boiler Service and Source Testing Relationship

Boiler service companies and source testing companies work together, but their roles are distinct. The service company maintains the equipment. The testing company measures what comes out of the stack.

The sequence matters. Burner tuning happens before the source test, not after. SCAQMD expects test results to reflect normal operating conditions.

Accurate Environmental Services works regularly with boiler service companies and their clients across the South Coast Air Basin. The typical workflow: the service company tunes the burner, AccuEnviro conducts the source test, and if results show elevated emissions, the service company adjusts and we retest. A well-tuned boiler that still can't meet its permit limit may need a burner retrofit -- information that's valuable to know before enforcement action arrives.

What a Boiler Source Test Involves

Most boiler tests use SCAQMD Method 100.1 with portable continuous gas analyzers measuring NOx, CO, and O2. Three valid runs are required, each lasting 15-30 minutes plus stabilization time. Total time onsite is typically 3-5 hours.

The crew connects analyzers to the sampling port, runs calibration checks, and collects data while the boiler operates at required conditions. O2 readings correct NOx and CO concentrations to the 3% O2 reference basis. Preliminary results are available the day of the test. Formal results follow in the source test report, submitted to SCAQMD within 60 days.

Don't Wait for the Inspector

The most common compliance issue with boiler source testing isn't a failing unit -- it's an overdue test. Facilities lose track of testing deadlines, personnel changes break institutional knowledge, and the next reminder comes in the form of an SCAQMD inspector asking for documentation.

A Notice of Violation for a late source test is avoidable. Track your testing deadlines. Set reminders at the six-month mark. Coordinate with your boiler service company and testing company early enough to allow for protocol approval, scheduling, and any maintenance that needs to happen first.

Frequently Asked Questions